Research On Cascaded-STATCOM Based On SVPWM

With the rapid development of modern power electronic technology,, pose a potential threat t o the safety, stability and economic operation of power system, influence the power quality serio usly and even endanger the safe operation of power system. So improving the power quality is a problem urgently to be solved. And reactive power as an important measure of power quality, the compensation of which is related to the safe and reliable operation of electrical equipments, the i mprovement of power factor and the reducement of Equipment capacity. Therefore, research on h ow to effectively compensate the reactive power is very significent. STATCOM is an ideal device used to compensate reactive power and is getting more attention.In high voltage, high power situations, the cascaded STATCOM often using the traditional SP WM modulation, has low dc voltage utilization rate, need multiple cascaded H bridge, but the cost is high and the reliability is low. Space vector modulation (SVPWM) technology with the advanta ges of improving the utilization ratio of voltage, is able to effectively reduce the number of H bri dge, but its computation is complicated when the level number is large, therefore, this paper introd uces an simplified SVPWM algorithm applied to the star connection chain STATCOM. the method, combined the two level space vector modulation technique with carrier phase shift modulation te chnology, can effectively improve the utilization rate of dc voltage and reduce the complexity of c alculation; what is more, the paper puts forward a dc voltage hierarchical control strategy, in order to realize the stability and balance of dc side of each H bridge. A simulation model is built in s oftware PSCAD, verifying the accuracy and feasibility of the modulation method and dc voltage control strategy. Finally a hardware device was designed and experiments were carried out, valida ting the simulationIn this paper, the main research contents are:firstly, different topologies of multilevel STATC OM and several modulation strategy are discussed;Secondly, the thesis introduced the space vect or modulation technology, researched the carrier phase shift technique combined with space vector modulation, and simplified the multilevel space vector modulation technology;Then the control stra tegy in the ac side and dc side of the STATCOM was studied; Finally in this paper, the design o f hardware and software of the cascade STATCOM based on SVPWM was introduced, and via the simulation and experimental waveforms, the control strategy,the hardware and the software syste m were verified rightly.Finally, this paper summarized the work, pointed out the shortages and prospected the future r esearch work.